Image capturing apparatus capable of intermittently capturing images, method for controlling the same, and storage medium

ABSTRACT

An image capturing apparatus for intermittently acquiring first images for use in generating a time lapse moving image, from among images corresponding to frames included in a moving image. The image capturing apparatus includes a target value setting unit configured to, based on a result of photometry, set a target value regarding an exposure when an image is acquired, a control value calculation unit configured to calculate a control value with respect to each frame regarding the exposure when brightness is changed toward the target value, and a control unit configured to control the exposure based on the control value. In a predetermined period before each first image is acquired, the control unit changes the exposure by a first degree of change, and outside the predetermined period, the control unit changes the exposure by a second degree of change different from the first degree of change.

BACKGROUND Field

The present disclosure relates to an image capturing apparatus capableof intermittently capturing images for acquiring a time lapse movingimage, a method for controlling the same, and a recording medium.

Description of the Related Art

Conventionally, there is known a technique for connecting, in order, aplurality of images acquired by intermittently capturing an image of anobject, thereby acquiring a moving image (a so-called time lapse movingimage) recorded by compressing temporal changes in the object.

As one of image capturing methods for acquiring such a time lapse movingimage, Japanese Patent Application Laid-Open No. 2015-142327 discusses atechnique for thinning images from a series of moving images forcompression, thereby generating a time lapse moving image (a movingimage-based interval image capturing technique).

SUMMARY

According to various embodiments, an image capturing apparatus forintermittently acquiring first images for use in generating a time lapsemoving image, from among images corresponding to frames included in amoving image acquired using an image capturing unit of the imagecapturing apparatus, is provided. The image capturing apparatus includesa photometric unit configured to perform photometry of an object, atarget value setting unit configured to, based on a result of thephotometry performed by the photometric unit, set a target valueregarding an exposure when an image is acquired using the imagecapturing unit, a control value calculation unit configured to calculatea control value with respect to each frame regarding the exposure whenbrightness is changed toward the target value set by the target valuesetting unit, and a control unit configured to control the exposurebased on the control value calculated by the control value calculationunit. In a predetermined period from predetermined timing before eachfirst image is acquired to when the first image is acquired, the controlunit changes the exposure by a first degree of change, and outside thepredetermined period, the control unit changes the exposure by a seconddegree of change different from the first degree of change. And in acase where the same amount of exposure is changed in the predeterminedperiod and outside the predetermined period, the exposure changes moresteeply by the first degree of change than by the second degree ofchange when an image is acquired.

Further features will become apparent from the following description ofexemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of a configuration ofa digital camera 1, which is an exemplary embodiment of an imagecapturing apparatus in which various embodiments are carried out.

FIG. 2 is a diagram illustrating an external view (a back view) of thecamera 1 according to the exemplary embodiment.

FIG. 3 is a flowchart illustrating an image capturing process in anormal moving image mode according to various embodiments.

FIG. 4 is a diagram illustrating a relationship between a frame rate anda predetermined number of frames N in which an exposure is changedtoward a target exposure in the normal moving image mode according tovarious embodiments.

FIG. 5 is a diagram illustrating first follow-up control of the exposureaccording to various embodiments.

FIG. 6 is a diagram illustrating changes in the exposure in Npredetermined frames in the normal moving image mode according tovarious embodiments.

FIGS. 7A and 7B are flowcharts illustrating an image capturing processin a time lapse mode according to a first exemplary embodiment.

FIG. 8 is a diagram illustrating a relationship between a frame rate anda predetermined number of frames N in which an exposure is changedtoward a target exposure in the time lapse mode according to the firstexemplary embodiment.

FIG. 9 is a diagram illustrating changes in the exposure in Npredetermined frames in the time lapse mode according to the firstexemplary embodiment.

FIG. 10 is a flowchart illustrating an image capturing process in a timelapse mode according to a second exemplary embodiment.

FIG. 11 is a diagram illustrating a relationship between a frame rateand a predetermined number of frames N in which an exposure is changedtoward a target exposure in the time lapse mode according to the secondexemplary embodiment.

FIG. 12 is a diagram illustrating changes in the exposure in Npredetermined frames in the time lapse mode according to the secondexemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

(Basic Configuration of Digital Camera 1)

Desirable exemplary embodiments are described below based on theattached drawings. FIG. 1 is a block diagram illustrating an example ofthe configuration of a digital camera (hereinafter referred to simply as“camera”) 1, which is a first exemplary embodiment of an image capturingapparatus in which various embodiments are carried out. One or more offunctional blocks illustrated in FIG. 1 may be achieved by hardware suchas an application-specific integrated circuit (ASIC) or a programmablelogic array (PLA), or may be achieved by a programmable processor suchas a central processing unit (CPU) or a microprocessor unit (MPU)executing software. Alternatively, one or more of the functional blocksmay be achieved by the combination of software and hardware. Thus, inthe following description, even in a case where different functionalblocks perform operations, the same hardware can perform the operations.

As illustrated in FIG. 1, the camera 1 according to the presentexemplary embodiment includes a camera main body 100 and a lens unit200. The lens unit 200 is configured to be freely attachable to anddetachable from the camera main body 100. With reference to FIG. 1, anillustrative description is given below of the configuration of thecamera 1 in the state where the lens unit 200 is connected (attached) tothe camera main body 100. The camera 1 may be configured such that thecamera main body 100 and the lens unit 200 are provided in an integratedmanner.

A camera control unit 101 is a camera control unit for performingoverall control of the components of the camera main body 100 andincludes a camera microcomputer (a camera CPU) (not illustrated).Further, the camera control unit 101 includes a built-in timer 101 a,which can measure time. The built-in timer 101 a is a real-time clockand measures time based on timer accuracy stored in advance in a memory102 and information of a time zone set in advance. The control contentof the camera control unit 101 will be described below with variousoperations. The memory 102 is a recording medium capable of recordingdata regarding the operation of the camera 1 and various pieces of dataacquired using the camera 1. The memory 102 according to the presentexemplary embodiment includes a read-only memory (ROM) area as anon-volatile memory and a random-access memory (RAM) area as a volatilememory.

A lens control unit 201 is a lens control unit for performing overallcontrol of the operation of the lens unit 200 and includes a lensmicrocomputer (a lens CPU) (not illustrated). The lens control unit 201can communicate with the camera control unit 101 via an interface (IF)in the state where the lens unit 200 is attached to the camera main body100. An imaging lens group 202 is a lens group including a plurality oflenses such as a shift lens, a zoom lens, and a focus lens and can guidea light beam representing an optical image of an object to the cameramain body 100 side. A diaphragm 203 is a light amount adjustment memberfor adjusting the amount of light regarding the speed of light passingthrough the inside of the imaging lens group 202. The driving of theimaging lens group 202 and the diaphragm 203 is controlled by the lenscontrol unit 201.

An image sensor 103 is an image capturing unit that employs a chargeaccumulation solid-state image sensor such as a complementarymetal-oxide-semiconductor (CMOS). The image sensor 103 photoelectricallyconverts a light beam incident on the image sensor 103 through the lensunit 200 and outputs analog image data. A shutter 104 is a blockingmember capable of blocking a light beam to be incident on the imagesensor 103. The shutter 104 can transition to a retracted state wherethe shutter 104 guides an incident light beam to the image sensor 103without blocking the light beam, and a blocking state where the shutter104 blocks an incident light beam.

An analog-to-digital (A/D) conversion unit 105 is an A/D conversion unitfor converting analog image data output from the image sensor 103 intodigital image data. An image processing unit 106 is an image processingunit for performing on the digital image data a resizing process such aspredetermined image interpolation or reduction, a color conversionprocess, and the process of calculating the numbers of pieces of pixeldata of saturated pixels and underexposed pixels. Further, the imageprocessing unit 106 is also a white balance (hereinafter referred to as“WB”) processing unit for performing a WB calculation process on thedigital image data. In the WB calculation process, the signal values ofrespective color signals (signals in the red, green, and blue (RGB)Bayer arrangement) corresponding to the image data output from the imagesensor 103 are multiplied by a predetermined WB coefficient, whereby itis possible to make WB adjustment on the image data according to variousconditions. The predetermined WB coefficient is a gain amount thatdiffers for each color signal. This WB coefficient is set based on, forexample, data stored by assuming predetermined ambient light in advance,data calculated based on a color temperature manually set by a user, ordata calculated by extracting the signal values of the respective colorsignals from the acquired image data.

A digital-to-analog (D/A) conversion unit 108 is a D/A conversion unitfor converting digital image data into analog image data for display. Amemory control unit 107 is a recording control unit for controlling theinput and output of image data to and from components such as the A/Dconversion unit 105, the image processing unit 106, and the D/Aconversion unit 108. An image capturing unit according to the presentexemplary embodiment may be configured to include the A/D conversionunit 105, the image processing unit 106, and the D/A conversion unit 108as components other than the image sensor 103.

A timing generator (hereinafter referred to as “TG”) 110 is a timinggeneration unit for transmitting timing regarding each operation of thecamera 1 to the components of the camera 1. For example, the TG 110 cangenerate various types of timing for accumulating charges in the imagesensor 103, changing the frame rate, and changing the state of theshutter 104.

A display unit 109 is a display unit including a thin-film transistor(TFT) liquid crystal display (LCD) (a thin-film-transistor-driven liquidcrystal display device) and can display analog image data for display.The display unit 109 can perform so-called live view display(hereinafter referred to as “LV display”) for sequentially displayingimage data acquired using the image sensor 103. The display unit 109 canalso display various pieces of information other than the acquired imagedata.

A shutter release button 111 is an image capturing instruction unit forgiving an instruction to start an image capturing preparation operationand an image capturing operation using the camera 1. The user changesthe shutter release button 111 to an SW1 state (e.g., half-presses theshutter release button 111), thereby giving an instruction to start animage capturing preparation operation. As a result, focus control andphotometric calculation are executed. Further, the user changes theshutter release button 111 to an SW2 state (e.g., full-presses theshutter release button 111), thereby giving an instruction to start animage capturing operation. As a result, a series of processes from thecapturing of an image of an object to the acquisition of the image isexecuted.

An operation unit 112 is an operation unit for inputting variousoperation instructions to the camera control unit 101. FIG. 2 is adiagram illustrating an external view (a back view) of the camera 1according to the exemplary embodiment of the present disclosure. Dashedportions illustrated in FIG. 2 indicate a first operation unit 112 a anda second operation unit 112 b. The first operation unit 112 a includesdirection indication buttons for giving an instruction to performvarious operations regarding the capturing of an image, and an LV buttonfor giving an instruction to execute and end LV display on the displayunit 109. The second operation unit 112 b includes a power switch and amode dial for setting an image capturing mode. If a capacitance touchpanel is employed as the display unit 109, the display unit 109 may beconfigured to function also as the shutter release button 111 and theoperation unit 112. In this case, the user can set the above items byoperating a user interface (UI) displayed on the display unit 109. Adisplay control unit 113 is a display control unit for performingoverall control of the display of image data using the display unit 109.According to an instruction from the camera control unit 101, thedisplay control unit 113 controls the selection of image data to bedisplayed on the display unit 109, and the turning on and off (thedisplay and non-display) of the display unit 109.

In the present exemplary embodiment, it is possible to set as the imagecapturing mode a plurality of modes such as a normal still image mode, anormal moving image mode (a second mode), and a time lapse mode (a firstmode). The normal still image mode is the mode of acquiring a singlepiece of image data (a still image) for recording. The normal movingimage mode is the mode of consecutively accumulating charges (capturingimages) using the image sensor 103, thereby acquiring a plurality ofconsecutive pieces of image data. These plurality of pieces of imagedata are connected together in order and displayed (or recorded),whereby it is possible to perform LV display and record a moving image.The time lapse mode is the mode of acquiring images (hereinafter, “timelapse images”) for use in generating a time lapse moving image, which isa moving image obtained by connecting intermittently acquired pieces ofimage data. These time lapse images are connected together in the orderof capturing (the order of acquisition), whereby it is possible togenerate a time lapse moving image. For description, time lapse imagesfor use in generating a time lapse moving image are referred to as“first images”, and images not for use in generating a time lapse movingimage are referred to as “second images”.

The details of the time lapse mode are described. In the time lapsemode, first, images are consecutively captured using the image sensor103, thereby acquiring a plurality of pieces of image data. Theplurality of acquired pieces of image data are used for LV display onthe display unit 109. From among the plurality of pieces of image data,time lapse images for use in generating a time lapse moving image areselected (set) based on image capturing intervals (intervals) set inadvance. Then, the set time lapse images are connected together in theorder of acquisition, thereby acquiring a time lapse moving image. Inthe normal moving image mode and the time lapse mode, chargeaccumulation rows of the image sensor 103 for capturing an object arereduced as compared with the normal still image mode (charges areaccumulated by thinning pixel rows). Further, in the time lapse mode,the image capturing intervals (the acquisition intervals of time lapseimages), the total number of times of acquisition, and the total time ofcapturing images can be optionally set by the user using the operationunit 112.

At this time, the reproduction time of a moving image acquired in thenormal moving image mode approximately coincides with the time requiredto capture images for acquiring the moving image. In contrast, thereproduction time of a time lapse moving image acquired in the timelapse mode is different from the time required to capture images foracquiring the moving image. In other words, the total time required toacquire a time lapse moving image is longer than the total time requiredto acquire a moving image for the same reproduction time in the normalmoving image mode. A time lapse moving image is a moving image obtainedby connecting intermittent pieces of image data acquired in a certainperiod. Thus, the reproduction time of the moving image is shorter thanthe total time of capturing images (the time from the start to the endof the capturing of images) for acquiring a single time lapse movingimage. Thus, a time lapse moving image is a moving image obtained bycompressing changes over time in an object.

A focus detection circuit 114 is a focus detection unit including afocus sensor (not illustrated) and for detecting the in-focus state ofan optical image corresponding to a light beam incident from the lensunit 200 side through a mirror (not illustrated). The focus detectioncircuit 114 can calculate information of the distance from the camera 1to a predetermined object based on a focus detection result. Thedetection result of the focus detection circuit 114 is used for control(focus control) of the lens position of a focus lens (not illustrated)included in the lens unit 200. In the present exemplary embodiment,focus control is executed by a phase difference detection method basedon the output of the focus detection circuit 114. Alternatively, theconfiguration may be such that focus control is executed by a contrastdetection method based on contrast information of image data. Further,in the present exemplary embodiment, the configuration is such thatfocus detection is executed using a focus sensor. Alternatively, theconfiguration may be such that focus detection is executed based on theoutput of the image sensor 103.

A photometric circuit 115 is a photometric unit including a photometricsensor (not illustrated) and for calculating the brightness (thephotometric value) of an optical image corresponding to a light beamincident from the lens unit 200 side through a photometric lens (notillustrated). The result of photometry performed by the photometriccircuit 115 is output to the camera control unit 101 and used forexposure control. A method for calculating a luminance value isspecifically described. First, acquired image data is divided into aplurality of blocks, and the average luminance values of the respectiveblocks are calculated. Then, the average luminance values of therespective blocks are integrated to acquire a representative luminancevalue. In the following description, this representative luminance valueis used as a photometric value for various types of processing andcontrol such as exposure control. In the present exemplary embodiment,the configuration is such that photometric calculation is executed usinga photometric sensor. Alternatively, the configuration may be such thatphotometric calculation is executed based on the output of the imagesensor 103.

A target value setting unit 116 is a target value setting unit forsetting target values of exposure control and WB adjustment based on theresult of photometry of an object. That is, the target value settingunit 116 is a unit for, when an image is acquired using the image sensor103, setting a target value regarding the brightness of the image, whichis a value as a target when the brightness is changed in a predeterminednumber of frames. In the present exemplary embodiment, the configurationis such that when a moving image is acquired in the normal moving imagemode and the time lapse mode, the photometric circuit 115 performsphotometry of an object to calculate a photometric value everypredetermined number of frames. The target value setting unit 116 sets atarget value of the exposure and a target value of WB adjustment basedon the photometric value.

At this time, the photometric value is a value that changes following achange in the luminance of the object. Thus, when a moving image isacquired, and if the exposure or the amount of WB adjustment is steeplychanged toward the target value, the degree of change in the brightnessbetween frames increases, and the brightness of the object in the movingimage unnaturally changes. This gives a sense of discomfort to the user.

In response, in the present exemplary embodiment, control valuesregarding the exposure and the amount of WB adjustment with respect toeach frame are provided so that changes in the exposure and WBadjustment are completed in the predetermined number of frames towardthe target values set by the target value setting unit 116.

A control value calculation unit 117 is a control value calculation unitfor, based on a target value set by the target value setting unit 116,calculating a control value regarding a change in the exposure or WBadjustment per frame. In other words, the control value calculation unit117 is a calculation unit for calculating, from the exposure and theamount of WB adjustment of the current frame, control values of theexposure and WB adjustment in the process (the predetermined number offrames) until previously set target values are achieved. That is, thecontrol value calculation unit 117 calculates a control value withrespect to each frame when the brightness is changed toward a set targetvalue, and these control values correspond to the setting values of thebrightness of the respective frames when the brightness is changed.

The control value calculation unit 117 can also set the control valuesof the respective frames in a predetermined period to different values.For example, when a moving image is acquired, and if exposure control isexecuted so that the exposure reaches an exposure target value in thesixth frame after the current frame, exposure control values of therespective frames may be varied between six frames.

An external recording medium 300 is a recording medium, such as a memorycard or a hard disk, capable of recording image data recorded in thememory 102. The external recording medium 300 is not limited to a memorycard insertable into and removable from the camera main body 100, andmay be an optical disc such as a digital versatile disc rewritable(DVD-RW) disc or a magnetic disk such as a hard disk. This is the basicconfiguration of the camera 1 according to the present exemplaryembodiment.

(Normal Moving Image Mode)

With reference to FIG. 3, an image capturing process in the normalmoving image mode is described below. FIG. 3 is a flowchart illustratingan image capturing process in the normal moving image mode according tothe present disclosure. In the normal moving image mode, in step S301,the camera control unit 101 determines whether an instruction to startthe capturing of an image is given. The process of step S301 is repeateduntil an instruction to start the capturing of an image is given.Examples of the image capturing start instruction in the normal movingimage mode include an instruction to acquire a moving image forrecording, and an instruction to acquire image data for use in LVdisplay on the display unit 109 without recording. In a case where LVdisplay on the display unit 109 is executed, an instruction to start LVdisplay corresponds to the image capturing start instruction.

If an image capturing start instruction is given (YES in step S301),then in step S302, the camera control unit 101 calculates a photometricvalue based on the output result of the photometric circuit 115. In stepS302, simultaneously, the camera control unit 101 increments a counter nto 0. Then, in step S303, based on the calculated photometric value, thetarget value setting unit 116 sets a target value of the exposure (atarget exposure) regarding exposure control.

Next, in step S304, based on the acquired target exposure and the framerate when a moving image is acquired, the control value calculation unit117 calculates control values of the exposure (control exposures) forexecuting first follow-up control. The first follow-up control is acontrol method for executing exposure control taking into account thegrade (the visual quality) of the moving image. With reference to FIG.4, the details of this are described below.

FIG. 4 is a diagram illustrating the relationship between the frame rateand a predetermined number of frames N (N is a natural number) in whichthe exposure is changed toward the target exposure in the normal movingimage mode according to the present disclosure. FIG. 4 illustrates acase where the exposure is changed by changing the aperture diameter ofthe diaphragm 203. In the present exemplary embodiment, the controlvalue calculation unit 117 divides the difference between the currentexposure and the target exposure by the predetermined number of frames Ncorresponding to the frame rate when a moving image is acquired, therebycalculating a control exposure per frame. For example, in a case wherethe frame rate of the moving image is set to 30 fps, the controlexposures of the respective frames are calculated so that the exposurereaches the target exposure in a total of six frames from the currentframe (after the target exposure is calculated in the present exemplaryembodiment). Referring back to FIG. 3, after the control exposures for Nframes are calculated, the camera control unit 101 sets thepredetermined number of frames N to the counter n (n=N), which indicatesthe number of remaining frames in which follow-up control of theexposure toward the target exposure is required.

Next, in step S305, the camera control unit 101 confirms the number ofremaining frames stocked in the counter n. Then, if the counter n isgreater than 0 (YES in step S305), the processing proceeds to step S306.In step S306, the camera control unit 101 waits for a verticalsynchronization signal (hereinafter referred to as a “VSYNC signal”) tobe generated by the TG 110. If the counter n is 0 (n=0) (NO in stepS305), the processing proceeds to step S302. In step S302, the cameracontrol unit 101 newly calculates a photometric value.

In step S306, the camera control unit 101 repeats the process until aVSYNC signal is detected. If a VSYNC signal is detected (YES in stepS306), the processing proceeds to step S307. Then, in step S307, basedon the calculated control exposures for N frames, the camera controlunit (control unit) 101 executes exposure control so that the exposurereaches the control exposure of an n-th frame which corresponds to thecounter n and in which an image is captured next. Specifically, in stepS307, the camera control unit changes exposure parameters such as thediaphragm value regarding the degree of opening of the aperture diameterof the diaphragm 203, the shutter speed regarding the chargeaccumulation time of the image sensor 103, and the imaging sensitivityregarding analog and digital gain amounts. Which exposure parameter isused to execute exposure control is set based on table data regardingexposure control stored in advance in the memory 102.

Next, in step S308, the camera control unit 101 executes thinningaccumulation of the image sensor 103 to capture an image of an object,thereby acquiring image data (hereinafter referred to simply as“images”). Then, in step S309, the camera control unit 101 displays theacquired images on the display unit 109 via the display control unit113. The images are sequentially displayed frame by frame on the displayunit 109 in the process of step S309, thereby executing LV display onthe display unit 109.

Next, in step S310, the camera control unit 101 determines whether amoving image is being recorded by the current processing. That is, instep S310, the camera control unit 101 determines whether only LVdisplay is being performed. If the camera control unit 101 determinesthat a moving image is not being recorded (NO in step S310), theprocessing proceeds to step S312. If the camera control unit 101determines that a moving image is being recorded (YES in step S310), theprocessing proceeds to step S311. Then, in step S311, the camera controlunit 101 executes the process of connecting the acquired images tosequentially obtain a moving image.

Next, in step S312, the camera control unit 101 subtracts 1 from thenumber of counts of the counter n (n=n−1) regarding the number ofremaining frames in which follow-up control toward the currently settarget exposure is executed. Then, in step S313, the camera control unit101 determines whether an instruction to end the capturing of an imageis given. Then, if the camera control unit 101 determines that aninstruction to end the capturing of an image is not given (NO in stepS313), the processing returns to step S305. If the camera control unit101 determines that an instruction to end the capturing of an image isgiven (YES in step S313), the acquisition of a moving image ends, andthe image capturing process in the normal moving image mode ends.Examples of the instruction to end the capturing of an image include aninstruction to end the acquisition of a moving image, and an instructionto end LV display on the display unit 109.

FIG. 5 is a diagram illustrating follow-up control (first follow-upcontrol) of the exposure according to various embodiments. Asillustrated in FIG. 5, in the first follow-up control in the normalmoving image mode, first, photometric calculation is executed for everyplurality of frames, and a target value for exposure control (a targetexposure) is set. Then, control exposures are set for N frames so thatthe brightness smoothly changes between N frames toward the set targetexposure. Then, exposure control is executed based on the controlexposures. Regarding the display and the recording of images, an imageread at the generation timing of a VSYNC signal is used for LV display,and this image is used as a recorded image.

FIG. 6 is a diagram illustrating changes in the exposure in thepredetermined number of frames, which is N, in the normal moving imagemode according to various embodiments. As illustrated in FIG. 6, theabove configuration is employed, whereby the camera 1 can smoothlychange the exposure toward the target exposure in each frame. Thus, itis possible to prevent an unnatural change in the brightness of a movingimage according to a change in the luminance of an object.

(Time Lapse Mode)

Next, with reference to FIGS. 7A and 7B, an image capturing process inthe time lapse mode is described. FIGS. 7 A and 7B are a flowchartillustrating an image capturing process in the time lapse mode accordingto the first exemplary embodiment of the present disclosure. In thenormal moving image mode, photometric calculation is executed for everyplurality of frames, and based on a photometric value calculated by thephotometric calculation, exposure control is smoothly executed in unitsof a plurality of frames. In this case, even if the brightness smoothlychanges in the entirety of a moving image acquired in the normal movingimage mode, the brightness of each frame (image) included in the movingimage may be different from the appropriate brightness of an object.That is, the images corresponding to the respective frames of the movingimage acquired in the normal moving image mode may include an imagecaptured and acquired in the state where the exposure does not reach thetarget exposure. Thus, if exposure control is executed in the time lapsemode similarly to the normal moving image mode, a control exposure maynot reach the target exposure at the timing for acquiring a time lapseimage.

At this time, a time lapse moving image is configured to be acquired bysetting (selecting) time lapse images from among images included in amoving image according to predetermined image capturing intervals(setting intervals), and connecting the set time lapse images. The timelapse moving image is represented by compressing temporal changes in anobject. Thus, the reproduction time of the moving image is shorter thanthe total time of capturing images. Thus, the number of times the imageof the object is captured to acquire a single time lapse moving image isgreater than in a case where a normal moving image is acquired. Forexample, to acquire a time lapse moving image for about a minute, it mayeven be necessary to capture images several hundred to several thousandtimes. Thus, to acquire a time lapse moving image using a mechanicalshutter (without using an electronic shutter), the number of times themechanical shutter is driven may reach the durable number of times soon.Further, in a case where almost all effective pixels of the image sensor103 are used for exposure without executing thinning accumulation,temporal differences occur from the first exposure row to the lastexposure row of the image sensor 103. Thus, distortion (shutterdistortion) may occur in an image acquired in a case where an image of amoving object is captured. In response to the above problems, theconfiguration in which time lapse images are selected from among imagesincluded in a moving image as in the present exemplary embodiment hasthe advantage of preventing the number of times the mechanical shutteris driven from reaching the durable number of times soon, the advantageof reducing distortion of an object occurring on an image when a movingobject is captured, and the advantage of allowing a reduction in thenumber of components of the mechanical shutter.

At this time, if images acquired based on follow-up control of theexposure in the normal moving image mode are simply used to generate atime lapse moving image, images having inappropriate brightness areconnected together, whereby the brightness between frames in the timelapse moving image unnaturally changes. Particularly, in a case whereexposure control is executed by changing the aperture diameter of thediaphragm 203, which is a mechanical component, unevenness of exposuremay occur in a frame (an image) acquired while the aperture diameter ofthe diaphragm 203 is changed. Further, it is difficult to accuratelyobtain the difference in exposure (the difference) from the targetexposure in a frame acquired while the aperture diameter of thediaphragm 203 is changed. Thus, it is difficult to perform gainadjustment or image processing on an image in which unevenness ofexposure occurs as described above, or an image of which the differencein exposure deviates from an assumed value, thereby correcting thebrightness of the image to accurate brightness.

Further, a time lapse moving image desired by the user can be generatedby connecting intermittently acquired images based on image capturingintervals optionally set by the user. Thus, if an image after a changein the exposure by exposure control is completed (after the exposurereaches the target exposure) is set as a time lapse image, imagecapturing intervals (acquisition intervals) may irregularly change.Thus, the time lapse moving image intended by the user may not beacquired. In response, in the present exemplary embodiment, a controlexposure with respect to each frame is set based on image capturingintervals, and based on the control exposure, follow-up control (secondfollow-up control) of the exposure is executed, thereby solving thisproblem. The details of this are described below.

As illustrated in FIGS. 7 A and 7B, based on the fact that aninstruction to record a time lapse moving image is given in the timelapse mode, the image capturing process is started. The process of stepS701 is similar to that of step S301 in the normal moving image mode,and therefore is not described here. In step S702, the camera controlunit 101 acquires lens information from the lens unit 200 attached tothe camera main body 100. The lens information at least includesinformation regarding the driving time (the change time of the aperturediameter) of the diaphragm 203 per unit time. Further, in a case wherethe camera 1 is a lens-integrated camera, the camera control unit 101reads information regarding the driving time of the diaphragm 203 storedin the memory 102. In the present exemplary embodiment, theconfiguration may be such that the lens information includes informationregarding the driving speed of the diaphragm 203.

Next, in step S703, based on the lens information acquired in step S702,the camera control unit 101 determines whether the shortest timerequired to drive the diaphragm 203 in a predetermined number of stepsin the Additive System of Photographic Exposure (APEX) unit is less thanor equal to a predetermined time. In the present exemplary embodiment,the camera control unit 101 calculates the shortest time (the shortestchange time) required to change the aperture diameter of the diaphragm203 by an amount corresponding to three exposure steps, and compares thecalculated shortest time with the predetermined time. As thepredetermined time, any value may be set. In the present exemplaryembodiment, as an average time required to change the aperture diameterof a diaphragm for various lenses in three steps (3 Ev in the APEXunit), 50 ms is set as the predetermined time. Further, in the presentexemplary embodiment, among a plurality of exposure parameters, thepredetermined time is set according to the time required to change theaperture diameter of a diaphragm, which requires a long time to changethe same amount of exposure. The present exemplary embodiment, however,is not limited to this. Alternatively, for example, the time required tochange another exposure parameter by a predetermined amount may be setas the predetermined time. Particularly, in a case where a neutraldensity (ND) filter, which is a mechanical component similarly to adiaphragm, is included, the time required to change the lighttransmittance of the ND filter by a predetermined amount may be set asthe predetermined time.

If the camera control unit 101 determines that the shortest change timeis longer than the predetermined time (NO in step S703), then in stepS704, the camera control unit 101 sets the current predetermined time tothe calculated shortest change time of the diaphragm 203. Further, ifthe camera control unit 101 determines that the shortest change time isless than or equal to the predetermined time (YES in step S703), theprocessing proceeds to step S705. The processes of steps S705 and S706are similar to those of steps S302 and S303 in the normal moving imagemode, and therefore are not described here.

Next, in step S707, the camera control unit 101 reads the previously setacquisition intervals (image capturing intervals) of time lapse imagesfrom the memory 102. Next, in step S708, based on the acquisitionintervals read in step S707 and the result of the time measurement ofthe built-in timer 101 a, the camera control unit (determination unit)101 determines whether the time until the acquisition of a time lapseimage is started next is less than or equal to the predetermined time.If the camera control unit 101 determines that the time until theacquisition of a time lapse image is started is longer than thepredetermined time (NO in step S708), the processing proceeds to stepS710. Further, if the camera control unit 101 determines that the timeuntil the acquisition of a time lapse image is started is less than orequal to the predetermined time (YES in step S708), the processingproceeds to step S709. The process of step S710 is similar to theprocess of step S304 in the normal moving image mode, and therefore isnot described here.

In step S709, based on the target exposure set in step S706, the controlvalue calculation unit 117 calculates control exposures (second controlexposures) for executing second follow-up control. Specifically, basedon the difference between the current exposure and the target exposure,the control value calculation unit 117 calculates control exposures fora predetermined number of frames N. At this time, the second follow-upcontrol is a control method for, taking into account the grade of a timelapse image, executing early follow-up (rapid follow-up) of the exposuretoward the target exposure according to the acquisition of a time lapseimage. The details of this are described below with reference to FIG. 8.

FIG. 8 is a diagram illustrating the relationship between the frame rateand the predetermined number of frames N in which the exposure ischanged toward the target exposure in the time lapse mode according tothe first exemplary embodiment of the present disclosure. FIG. 8illustrates a case where the exposure is changed by changing theaperture diameter of the diaphragm 203.

As illustrated in FIG. 8, in the time lapse mode, outside apredetermined period based on the timing for acquiring a time lapseimage, an operation similar to that in the normal moving image mode isexecuted. That is, in the time lapse mode, outside the predeterminedperiod, similarly to the normal moving image mode, the control exposuresof the respective frames are set so that LV display smoothly changes.Within the predetermined period based on the acquisition timing of atime lapse image (which corresponds to gray filled portions in FIG. 8),the exposure is steeply changed toward the target exposure so that thetime lapse image has appropriate brightness. Then, exposure control isexecuted based on the set control exposures. Regarding the display andthe recording of images, an image read at the generation timing of aVSYNC signal is used for LV display, and from among frames used for thedisplay, time lapse images set based on the image capturing intervalsare used to generate a time lapse moving image.

The above configuration is specifically described. By a method similarto that in the process of step S304, the control value calculation unit117 calculates the control exposures of frames corresponding to theperiod (outside the predetermined period) from the previous acquisitiontiming of a time lapse image to a predetermined time before the nextacquisition timing. This predetermined time is the same as thepredetermined time used in the determination in step S708.

In contrast, the control value calculation unit 117 sets the controlexposures of the respective frames corresponding to the period (thepredetermined period) from the predetermined time before the nextacquisition timing to the next acquisition timing to the same value asthat of the target exposure. In other words, in the time lapse mode, ata plurality of types of timing for executing photometric calculation,the target exposure set based on photometric calculation executedimmediately before a time lapse image is acquired, and the controlexposures of the respective frames have the same value. In this case,when the same amount of exposure is changed, the exposure changes moresteeply by the degree of change (a first degree of change) in theexposure of the frames corresponding to the predetermined period than bythe degree of change (a second degree of change) in the exposure of theframes corresponding to the period outside the predetermined period.However, this does not apply to a case where the process of step S710 isexecuted as a result of the determination in step S708. Further, thedegree of change in the exposure of the respective frames in the normalmoving image mode is approximately the same as the second degree ofchange.

FIG. 9 illustrates this state. FIG. 9 is a diagram illustrating changesin the exposure in N predetermined frames in the time lapse modeaccording to the first exemplary embodiment of the present disclosure.As illustrated in FIG. 9, the above configuration is employed, wherebyin the present exemplary embodiment, the exposure can reach the targetexposure before the acquisition timing of a time lapse image. Thus, thecamera 1 according to the present exemplary embodiment can acquire atime lapse image having appropriate brightness for the luminance of anobject (a time lapse image for which the target exposure is set). Thus,it is possible to prevent an unnatural change in the brightness of atime lapse moving image. In the examples illustrated in FIGS. 8 and 9,temporal changes in the aperture diameter of the diaphragm 203 in thesecond follow-up control are ignored on the assumption that the aperturediameter of the diaphragm 203 can be immediately changed. Actually,however, a certain time is required to change the aperture diameter ofthe diaphragm 203 to a target aperture diameter.

Referring back to FIGS. 7 A and 7B, the processes of steps S711 to S716are similar to the processes of steps S305 to S309 in the normal movingimage mode, and therefore are not described here. Next, in step S717,according to the result of the time measurement of the built-in timer101 a based on the image capturing intervals set in advance, the cameracontrol unit 101 determines whether the current frame is a framecorresponding to the acquisition timing of a time lapse image.

If the camera control unit 101 determines that the current frame is notthe acquisition timing of a time lapse image (NO in step S717), theprocessing proceeds to step S719. If the camera control unit 101determines that the current frame is the acquisition timing (YES in stepS717), the processing proceeds to step S718. Then, in step S718, thecamera control unit 101 executes the process of connecting the acquiredtime lapse images in the order of acquisition (capturing) tosequentially obtain a moving image. The process of step S719 is similarto the process of step S312 in the normal moving image mode, andtherefore is not described here.

Next, in step S720, the camera control unit 101 determines whether aninstruction to end the acquisition of a time lapse moving image isgiven. An instruction to end the acquisition of a time lapse movingimage is given in a case where a condition set in advance for ending theacquisition of a time lapse moving image is satisfied, in addition to acase where an instruction to end the capturing of an image is givenaccording to an operation of the user. In this case, in step S720, thecamera control unit 101 determines whether the number of times ofacquisition (or the image capturing time) of a time lapse image reachesthe total number of times of acquisition (or the total image capturingtime) set in advance. Then, if the camera control unit 101 determinesthat the number of times of acquisition of a time lapse image does notreach the total number of times of acquisition (NO in step S720), theprocessing returns to the process of step S712. If the camera controlunit 101 determines that the number of times of acquisition reaches thetotal number of times of acquisition (YES in step S720), the imagecapturing process ends. This is the image capturing process in the timelapse mode according to the present exemplary embodiment.

As described above, in the time lapse mode, normally, taking intoaccount the visual quality of LV display, the camera 1 according to thepresent exemplary embodiment smoothly changes the exposure in responseto a change in the luminance of an object. Then, taking into account thegrade of a time lapse moving image, the camera 1 steeply changes theexposure toward a target exposure corresponding to the luminance of theobject according to the acquisition timing of a time lapse image. Withthis configuration, in the time lapse mode, the camera 1 according tothe present exemplary embodiment can prevent a reduction in the grade ofLV display as much as possible, while preventing a reduction in thegrade of a time lapse image. Particularly, even in a case where theexposure is changed by changing the aperture diameter of the diaphragm203, it is possible to prevent unevenness of exposure from occurring ina single frame according to temporal changes in the aperture diameter.Thus, in a case where the above configuration is carried out, it ispossible not only to prevent a reduction in the grade of an acquiredtime lapse image, but also to acquire, taking into account subsequentimage processing, a time lapse image in which unevenness of exposuredoes not occur. Thus, the camera 1 according to the present exemplaryembodiment can prevent an unnatural change in the brightness of aportion corresponding to an object in a time lapse moving image.

Next, with reference to FIGS. 10 to 12, a description is given of asecond exemplary embodiment of the image capturing apparatus in whichvarious embodiments are carried out. In the first exemplary embodiment,the configuration is such that in the time lapse mode, a time lapseimage acquired while images are sequentially displayed (subjected to LVdisplay) is also used for LV display. In contrast, in the presentexemplary embodiment, a time lapse image is not used for LV display, anda control exposure is temporarily matched to a target exposure accordingto the acquisition of the time lapse image, whereby it is possible toprevent an unnatural change in the brightness in LV display. The detailsof this are described below. A digital camera (hereinafter referred tosimply as “camera”) 1, which is the image capturing apparatus accordingto the present exemplary embodiment, has similar configuration to thatin the first exemplary embodiment. Thus, the components of the camera 1are designated by the same numbers as those in the first exemplaryembodiment.

FIG. 10 is a flowchart illustrating an image capturing process in thetime lapse mode according to the second exemplary embodiment of thepresent disclosure. As illustrated in FIG. 10, based on the fact that aninstruction to record a time lapse moving image is given in the timelapse mode, the image capturing process is started. The processes ofsteps S1001 to S1007 are similar to the processes of steps S301 to S307in the normal moving image mode in the first exemplary embodiment, andtherefore are not described here.

In step S1008, according to the result of the time measurement of thebuilt-in timer 101 a based on the image capturing intervals set inadvance, the camera control unit 101 determines whether the currentframe is a frame corresponding to the acquisition timing of a time lapseimage. If it is determined that the current frame is not the acquisitiontiming of a time lapse image (NO in step S1008), the processing proceedsto step S1009. The processes of steps S1009 and S1010 are similar tothose of steps S307 and S308 in the first exemplary embodiment, andtherefore are not described here. If, on the other hand, it isdetermined that the current frame is the acquisition timing of a timelapse image (YES in step S1008), the processing proceeds to step S1011.

In step S1011, the camera control unit 101 determines whether thecontrol exposure will reach the calculated target exposure in the nextframe. Then, if it is determined that the control exposure will reachthe target exposure (YES in step S1011), the processing proceeds to stepS1009. If it is determined that the control exposure will not reach thetarget exposure (NO in step S1011), the processing proceeds to stepS1012.

In step S1012, the camera control unit 101 changes the shutter speed(Tv) and the imaging sensitivity (the International Organization forStandardization (ISO) sensitivity) according to the target exposure,thereby executing exposure control. In the exposure control in thiscase, a target exposure is temporarily set for the time lapse imagewithout taking into account the visual quality of LV display. Thus, evenwhile exposure control is executed so that the exposure smoothly changesaccording to N frames, exposure control is executed so that the exposuretemporarily reaches the target exposure at the acquisition timing of atime lapse image. The reason why exposure control is executed usingexposure parameters such as the shutter speed and (or) the imagingsensitivity is that the time required to change approximately the sameexposure is shorter using the shutter speed or the imaging sensitivitythan using the diaphragm value. With this configuration, it is possibleto cause the actual exposure to reach a target exposure in a short timeless than a single frame in the present exemplary embodiment.

FIG. 11 is a diagram illustrating the relationship between the framerate and the predetermined number of frames N in which the exposure ischanged toward the target exposure in the time lapse mode according tothe second exemplary embodiment of the present disclosure. FIG. 12 is adiagram illustrating changes in the exposure in the predetermined numberof frames, which is N, in the time lapse mode according to the secondexemplary embodiment of the present disclosure. FIGS. 11 and 12illustrate a case where the exposure is changed by changing thediaphragm value in the period except the acquisition timing of a timelapse image, and changing the shutter speed and the imaging sensitivityat the acquisition timing of a time lapse image.

As illustrated in FIGS. 11 and 12, in the time lapse mode, outside apredetermined period based on the timing for acquiring a time lapseimage, the camera 1 according to the present exemplary embodimentexecutes exposure control similar to that in the normal moving imagemode in the first exemplary embodiment. That is, outside thepredetermined period, the control exposures of the respective frames (Nframes) are set so that the brightness smoothly changes in LV displayaccording to a change in the luminance of an object. In contrast, withinthe predetermined period, exposure control is executed so that asillustrated in FIGS. 11 and 12, the exposure steeply changes so that acontrol exposure temporarily reaches the target exposure.

Referring back to FIG. 10, in step S1013, similarly to steps S308 andS715, the camera control unit executes thinning accumulation of theimage sensor 103 to capture an image of an object, thereby acquiringthinned images. Then, in step S1014, the camera control unit 101 doesnot use the thinned images (time lapse images) acquired in step S1013for LV display, and selects an image signal displayed in the most recentframe again for LV display (a frame stop). The processes of steps S1015to S1017 are similar to the processes of steps S716, S719, and S720 inthe first exemplary embodiment, and therefore are described here.

As a control exposure temporarily changed according to the acquisitiontiming of a time lapse image, a control exposure is set again accordingto the acquisition of image data corresponding to the next frame so thatthe exposure changes by approximately the same degree of change as thatin the normal moving image mode. At this time, as illustrated in FIGS.11 and 12, a control exposure is set taking into account an exposurecorresponding to a case where the exposure is changed similarly to thenormal moving image mode in the predetermined period in view of theperiod in which the frame stop is performed. In addition to this, theconfiguration may be such that the control exposure is changed back tothat before the change. In this case, control exposures for N frames arecalculated in view of the period in which the frame stop is performed.

In step S1018, according to the image capturing end instruction, thecamera control unit 101 connects the already acquired time lapse imagesin the order of acquisition to generate a time lapse moving image. Thisis the time lapse mode in the present exemplary embodiment. Thepredetermined period in the present exemplary embodiment is a periodcorresponding to a single frame indicating each of the generationintervals of a VSYNC signal (gray filled portions in FIG. 11).Alternatively, another period may be set as the predetermined period.

As described above, the camera 1 according to the present exemplaryembodiment is configured to temporarily change the shutter speed and theimaging sensitivity according to the timing for acquiring a time lapseimage, thereby performing control so that the brightness of the imagereaches a target exposure. Then, the camera 1 according to the presentexemplary embodiment is configured not to use for LV display the imageacquired in this temporary change in the exposure. This configuration isemployed, whereby the camera 1 according to the present exemplaryembodiment can prevent an unnatural change in the brightness of anobject in LV display, while acquiring time lapse images. Then, thisconfiguration is employed, whereby the camera 1 according to the presentexemplary embodiment can prevent an unnatural change in the brightnessof the object also in a time lapse moving image generated by connectingthe time lapse images in order.

While the desirable exemplary embodiments of the present disclosure havebeen described, the present disclosure is not limited to these exemplaryembodiments, but embodiments may include various modifications andchanges without departing from the spirit and scope of the invention.For example, in the above exemplary embodiments, the configuration issuch that a time lapse moving image is generated within the camera 1.Alternatively, the configuration may be such that a time lapse movingimage is generated in an external device or on a computer network.

In the above exemplary embodiments, a case has been described whereoutside the predetermined period, the exposure is changed by changingthe aperture diameter of the diaphragm 203. The configurations of theabove exemplary embodiments, however, are effective also in a case wherethe exposure is changed using another exposure parameter.

Further, in the above exemplary embodiments, as illustrated in FIG. 9,all the control exposures corresponding to N predetermined frames in asingle cycle that overlaps the acquisition timing of a time lapse imageare set to the same value as that of the target exposure. The exemplaryembodiments, however, are not limited to this. For example, the valuesof the respective control exposures of N predetermined frames thatoverlap the acquisition timing of a time lapse image may be differentfrom each other so long as the exposure can reach the target exposurebefore the acquisition of the time lapse image. In this case, thecontrol exposures are changed step by step until the frame in which thetime lapse image is acquired, whereby it is possible to moderate thedegree of change in the exposure. Thus, it is possible to prevent anabrupt change in the brightness between frames in LV display.

Further, in the above exemplary embodiments, a description has beengiven of the configuration in which the exposure is changed when animage of an object is captured. The exemplary embodiments, however, arenot limited to this. For example, the configuration may be such that inthe time lapse mode, images are acquired by executing the firstfollow-up control, giving priority to the grade of LV display, and thedigital gain amounts of, among the acquired images, images for use ingenerating a time lapse moving image are changed. In this case, it isdesirable that every time an image of an object is captured (or everytime a time lapse image is acquired at a predetermined intervaldetermined in advance), information regarding the difference between acontrol exposure and a target exposure should be stored in associationwith the image. With this configuration, when a time lapse moving imageis generated, it is possible to set the digital gain amounts of timelapse images to optimal values based on this information.

Further, in the above exemplary embodiments, follow-up control of theexposure has been described. An approximately similar configuration isalso applicable to follow-up control of WB adjustment. For example, inFIGS. 7 A and 7B, in step S704, WB calculation is performed. In stepS705, based on the result of the calculation, a target value for WBadjustment is set. In step S709 or S710, control values for WBadjustment are calculated. In this case, when the same amount of WBadjustment is made, the degree of WB adjustment (the degree of change)in the predetermined period is steeper using second control values forWB adjustment calculated in step S709 than using first control valuesfor WB adjustment calculated in step S710. A predetermined timeregarding WB adjustment may be set to the shortest time required toexecute a predetermined amount of WB adjustment in the predeterminedperiod. With this configuration, it is possible to acquire a time lapseimage in which the brightness of an object is appropriately subjected toWB adjustment. Thus, it is possible to prevent an unnatural change inthe brightness of the object in a time lapse moving image.

Further, in the above exemplary embodiments, the configuration is suchthat the components included in the camera 1, such as the camera controlunit 101, the memory 102, the image processing unit 106, and the memorycontrol unit 107, operate cooperatively with each other, therebycontrolling the operation of the camera 1. The exemplary embodiments,however, are not limited to this. Alternatively, the configuration maybe such that, for example, a (computer) program according to the flowsillustrated in FIGS. 3 and 7 is stored in advance in the memory 102.Then, the camera control unit 101 including a microcomputer executes theprogram, thereby controlling the operation of the camera 1. Further, asthe form of the program, any form such as an object code, a programexecuted by an interpreter, or script data supplied to an operatingsystem (OS) can be employed so long as the employed form has thefunction of a program. Further, as a recording medium for supplying theprogram, a magnetic recording medium such as a hard disk or a magnetictape, or an optical or magneto-optical recording medium may be employed.

Further, in the above exemplary embodiments, a digital camera has beendescribed as an example of the image capturing apparatus in whichvarious embodiments are carried out. The exemplary embodiments, however,are not limited to this. Alternatively, for example, the configurationmay be such that an image capturing apparatus other than a digitalcamera, such as a portable device, e.g., a digital video camera or asmartphone, a wearable terminal, or a security camera, may be employed.

Other Embodiments

Embodiment(s) of the present disclosure can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While exemplary embodiments have been described, it is to be understoodthat the disclosure is not limited to the disclosed exemplaryembodiments. The scope of the following claims is to be accorded thebroadest interpretation so as to encompass all such modifications andequivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2016-126971, filed Jun. 27, 2016, and Japanese Patent Application No.2017-014850, filed Jan. 30, 2017, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. An image capturing apparatus for intermittentlyacquiring first images for use in generating a time lapse moving image,from among images corresponding to frames included in a moving imageacquired using an image capturing unit of the image capturing apparatus,the image capturing apparatus comprising: a photometric unit configuredto perform photometry of an object; a target value setting unitconfigured to, based on a result of the photometry performed by thephotometric unit, set a target value regarding an exposure when an imageis acquired using the image capturing unit; a control value calculationunit configured to calculate a control value with respect to each frameregarding the exposure when brightness is changed toward the targetvalue set by the target value setting unit; and a control unitconfigured to control the exposure based on the control value calculatedby the control value calculation unit, wherein in a predetermined periodfrom a predetermined timing before each first image is acquired to whenthe first image is acquired, the control unit changes the exposure by afirst degree of change, and outside the predetermined period, thecontrol unit changes the exposure by a second degree of change differentfrom the first degree of change, and wherein in a case where the sameamount of exposure is changed in the predetermined period and outsidethe predetermined period, the exposure changes more steeply by the firstdegree of change than by the second degree of change when an image isacquired.
 2. The image capturing apparatus according to claim 1, whereinthe predetermined period is a period required to change the exposure bya predetermined amount when an image is acquired using the imagecapturing unit.
 3. The image capturing apparatus according to claim 2,wherein the predetermined period is a period required to change anaperture diameter of a diaphragm corresponding to a predetermined numberof steps when an image is acquired using the image capturing unit. 4.The image capturing apparatus according to claim 3, wherein thepredetermined period is set based on information regarding a drivingtime of the diaphragm per unit time, the information acquired from alens unit connected to the image capturing apparatus.
 5. The imagecapturing apparatus according to claim 1, further comprising adetermination unit configured to determine whether a time until timingfor acquiring the first images next is longer than the predeterminedperiod, wherein in a case where the determination unit determines thatthe time until the timing for acquiring the first images next is longerthan the predetermined period, the control unit changes the exposure bythe second degree of change also in the predetermined period.
 6. Theimage capturing apparatus according to claim 5, wherein in a case wherethe determination unit determines that the time until the timing foracquiring the first images next is less than or equal to thepredetermined period, the control unit changes the exposure by the firstdegree of change in the predetermined period and changes the exposure bythe second degree of change outside the predetermined period.
 7. Theimage capturing apparatus according to claim 1, wherein the imagecapturing apparatus can set a first mode for intermittently acquiringthe first images, and a second mode for consecutively acquiring secondimages not for use in generating a time lapse moving image, withoutacquiring the first images, wherein the control unit changes theexposure by the second degree of change in the second mode, and whereinan image capturing time of an object required to generate a moving imagefor the same reproduction time is longer in a case of a time lapsemoving image acquired in the first mode than in a case of a moving imageobtained by connecting a plurality of images acquired in the secondmode.
 8. The image capturing apparatus according to claim 1, wherein thecontrol value calculation unit calculates control values of respectiveframes corresponding to the predetermined period so that the controlvalues are the same value as the target value set by the target valuesetting unit, and the control value calculation unit calculates controlvalues of respective frames corresponding to a period outside thepredetermined period so that the control values change step by step in apredetermined number of frames toward the target value set by the targetvalue setting unit.
 9. The image capturing apparatus according to claim1, further comprising a display control unit configured to sequentiallydisplay, on a display unit, images acquired using the image capturingunit, wherein the display control unit performs control so that thefirst images are not used for sequential display.
 10. The imagecapturing apparatus according to claim 9, wherein the predeterminedperiod is a period required to acquire each first image.
 11. The imagecapturing apparatus according to claim 10, wherein the control unittemporarily changes a parameter regarding the exposure other than adiaphragm value in the predetermined period.
 12. A method forcontrolling an image capturing apparatus, the method for intermittentlyacquiring first images for use in generating a time lapse moving image,from among images corresponding to frames included in a moving imageacquired using an image capturing unit of the image capturing apparatus,the method comprising: performing photometry of an object; based on aresult of the photometry, setting a target value regarding an exposurewhen an image is acquired using the image capturing unit; calculating acontrol value with respect to each frame regarding the exposure whenbrightness is changed toward the set target value; and controlling theexposure based on the calculated control value, wherein in apredetermined period from predetermined timing before each first imageis acquired to when the first image is acquired, the exposure is changedby a first degree of change, and outside the predetermined period, theexposure is changed by a second degree of change different from thefirst degree of change, and wherein in a case where the same amount ofexposure is changed in the predetermined period and outside thepredetermined period, the exposure changes more steeply by the firstdegree of change than by the second degree of change when an image isacquired.
 13. A non-transitory computer-readable storage medium storinginstructions for causing a computer to execute a process for controllingan image capturing apparatus, the process for intermittently acquiringfirst images for use in generating a time lapse moving image, from amongimages corresponding to frames included in a moving image acquired usingan image capturing unit of the image capturing apparatus, the processcomprising: performing photometry of an object; based on a result of thephotometry, setting a target value regarding an exposure when an imageis acquired using the image capturing unit; calculating a control valuewith respect to each frame regarding the exposure when brightness ischanged toward the set target value; and controlling the exposure basedon the calculated control value, wherein in a predetermined period frompredetermined timing before each first image is acquired to when thefirst image is acquired, the exposure is changed by a first degree ofchange, and outside the predetermined period, the exposure is changed bya second degree of change different from the first degree of change, andwherein in a case where the same amount of exposure is changed in thepredetermined period and outside the predetermined period, the exposurechanges more steeply by the first degree of change than by the seconddegree of change when an image is acquired.